1. Field of the Invention
The present invention relates to exchange coupling films including an antiferromagnetic layer and a ferromagnetic layer between which an exchange coupling field (Hex) occurs to align the magnetization of the ferromagnetic layer in a predetermined direction, and also to magnetic sensing elements including the exchange coupling films. In particular, the present invention relates to an exchange coupling film including a ferromagnetic layer made of CoFe and an antiferromagnetic layer made of IrMn to provide a larger exchange coupling field (Hex), and also to a magnetic sensing element including the exchange coupling film.
2. Description of the Related Art
FIG. 6 is a partial sectional view of a conventional magnetic sensing element (spin-valve thin-film element), taken along a plane parallel to a surface facing a recording medium.
In FIG. 6, a seed layer 14 is made of, for example, NiFeCr. An antiferromagnetic layer 30, a pinned magnetic layer 31, a nonmagnetic material layer 32, a free magnetic layer 33, and a protective layer 7 are sequentially formed on the seed layer 14.
This type of spin-valve thin-film element generates an exchange coupling field between the antiferromagnetic layer 30 and the pinned magnetic layer 31 by performing heat treatment to pin the magnetization of the pinned magnetic layer 31 in the height direction (the Y direction in the drawing).
Hard bias layers 5 are formed on the sides of the multilayer film including the above layers. These hard bias layers 5 generate a longitudinal bias field to align the magnetization of the free magnetic layer 33 in a track width direction (the X direction in the drawing).
Electrode layers 8 are formed on the hard bias layers 5. These electrode layers 8 allow a sense current to flow mainly through the pinned magnetic layer 31, the nonmagnetic material layer 32, and the free magnetic layer 33.
The antiferromagnetic layer 30 is made of IrMn while the pinned magnetic layer 31 is made of CoFe. This type of magnetic sensing elements are disclosed in Japanese Unexamined Patent Application Publication Nos. 9-237716 (Page 7 and FIG. 10 of the publication), 9-148132 (Page 8 and FIG. 10 of the publication), and 2002-208120 (Page 11 of the publication).
The above publications disclose magnetic sensing elements including an antiferromagnetic layer made of IrMn and a pinned magnetic layer (ferromagnetic layer) made of CoFe, though the composition of CoFe disclosed is only Co90Fe10. If a pinned magnetic layer made of Co90Fe10 is formed on an antiferromagnetic layer made of PtMn, a sufficiently large exchange coupling field occurs to pin the magnetization of the pinned magnetic layer. If, however, the antiferromagnetic layer is made of IrMn, the exchange coupling field is small. This results in a higher possibility of inversion of the magnetization of the pinned magnetic layer in a process of producing a magnetic sensing element. This problem is serious particularly for top spin-valve giant magnetoresistive (GMR) elements, in which an antiferromagnetic layer is formed on a pinned magnetic layer.